Pulse modulator



I Oct. 25, D Y. KEIM PULSE MODULATOR Filed May 24, 1943 FIG. 4.

FIG. 3.

INVENTOR DAVID Y. KEIM ATTORNEY Patented Oct. 25, 1949 PULSE MODULATORDavid Y. Kcim, Garden City, N. Y., assignor to The Sperry Corporation,a. corporation of Delaware Application May 24, 1943, Serial No. 488,128

'9 Claims. 1

My invention relates broadly to modulators and, more specifically, topulse modulators for ultra high frequency oscillators.

Modern ultra high frequency technique requires in some applications theoperation of certain types of ultra high frequency osciliators such asthe magnetron at comparatively high power levels. Since the maximumpower levclat which continuous operation of these oscillatorsmay besafely maintained is limited by design, it is common practice to operatethe apparatus with high power inputs for shcrt periods only, therebykeeping the average operating conditions within the limits of safety.

When thus operated, the oscillator is "pulsed by a high power levelsurge, the period of which determines the on time of the oscillator inwhich signals are transmitted. The interval between pulses, which islong compared with their period, then fixes the time the apparatus isturned off before signals are again transmitted. Modulators forsupplying this high power pulse have taken two forms, namely, the vacuumtube type and the spark gap generator type.

The spark gap generator is not adaptable to systems in which theoscillator is triggered from a synchronizing source, but is used wherethe transmitter itself delivers the trigger pulse because of one of itsinherent characteristics, termed in the art as jitter," which does notpermit accurate timing of the spark. Because of high power requirements,the vacuum tube modulator has heretofore been rather bulky, which isequally objectionable.

It is therefore an object of my invention to provide a vacuum tube pulsemodulator whichis simple in design, small and compact in structure, andadaptable to portable applications where minimum weight is essential.

Another object of my invention is to provide a method and apparatus forcoupling a high power source and an ultra high frequency oscillatorwhich does not require a direct current charging path for the filteringcondenser in its power supply nor the damping devices made necessary bysuch a charging path.

A further object of my invention is the arrangement of a vacuum tubepulse modulator circuit in which a plurality of power pulsing tubes maybe reliably triggered without distortion of the triggering pulse.

A still further object of my invention is to provide a pulse modulatorin which a power pulsing network is inductively connected to an ultrahigh frequency oscillator.

2 Another purpose of my invention is to provide a high power vacuum tubepulse modulator in which medium power tubes may be used.

It is also an object of my invention to provide apparatus for accuratelytiming a high power pulse.

Yet another purpose of my invention is to provide a pulse modulator inwhich the potential of interruptively discharged cherry is increased andsimultaneously transferred by induction.

These and other objects of my invention will become manifest as thedescription proceeds.

In carrying out my invention in a preferred embodiment thereof. I employa line controlled blocking oscillator to drive a plurality of powerpulsing tubes for controlling the time duration of pulse modulation.When the pulsing tubes receive a high amplitude pulse from the blockingoscillator, the period of which is determined by the length of asimulated transmission line connected inthe grid circuit of the blockingoscillator, a charging condenser in the power supply network of thecircuit is caused to discharge through the primary Winding of an autotransformer used for coupling the power supply to the oscillator whichis to be pulsed. The secondary winding of this transformer then deliversthe modulating pulse.

In addition to acting as a coupling means for the power tubes and theirload, the auto transformer also performs the function of animpedance-matching device which is necessitated by the number of powertubes employed in the switching network of the circuit. Here the numberof tubes used is dependent upon the currentconducting requirements ofthis branch.

The fact that a number of power pulsing tubes are necessarily used alsomakes it impossible to drive these tubes directly and reliably by theoutput of the blocking oscillator. By connecting a cathode follower,which acts as a buffer stage, between these elements of the circuit, itis possible, however, to drive the tubes without distortion of thetriggering pulse.

Also by using my improved coupling method, it is possible for me to usemedium voltage tubes in the switching network having oxide-coatedcathodes and to use these tubes in conjunction with a. high-poweredsystem. This makes unnecessary the use of the gas-filled 'Ihyratronsandthe bulky, less efficienthigh voltage tubes used in previous systems.

This method of coupling further simplifies the circuit, since it makesit unnecessary to provide a direct current shunt path across the ultrahigh frequency oscillator. Consequently, I am able to omit theinductance coils and dampin devices used in prior systems.

By reducing the size and number of parts, I have produced a vacuum tubemodulator which is adaptable to portable needs where the weight of theapparatus must be kept at a minimum.

A more comprehensive understanding of my invention may be obtained fromthe following detailed description, when taken together with theaccompanying drawing, in which like reference numerals have been usedthroughout to designate like parts and in which,

Fig. 1 is a circuit diagram of an embodiment of my invention.

Fig. 2 is a representative showing of prior art methods of coupling highpower sources with ultra high frequency oscillators.

Fig. 3 is a simplified showing of my improved coupling means forcoupling power tubes with their load, and

Fig. 4 is a diagram showing the relationship between the power linefrequency and pulse repetition rate.

In the embodiment illustrated in Fig. 1, a square trigger pulse isapplied to the input terminals Ill of the circuit, from which point itis fed to a connection II on the simulated transmission line |2. Thisline is made up of sections comprising inductance coils l3 andcapacitors M and is used to control the period of a pulse generated by apulse amplifier network IS in whose control grid circuit it isconnected.

The network |5 serves as a blocking oscillator transformer and comprisesan electronic discharge device IB, which may take the form of a doubletetrode, a multiple winding transformer l1, and the delay line l2. Agrid winding |8 of the transformer l'l has a resistor I9 connected inparallel therewith and serves as a conductor for transmitting thetrigger pulse from the delay line l2 to the grids 2| of the doubletetrode it through grid resistors 22. A common winding 23 of thetransformer I1 is inductively connected with the grid winding l8 andoutput winding 24, the latter being provided to obtain a positivevoltage pulse as the output of the blocking oscillator transformer.Resistors l9 and 25, in parallel with windings l8 and 24, provide fixedloading for these windings and in performing this function improve thewave form of the pulse output of the network.

Positive voltage is supplied to the anodes 26 of tube l6, whoseelectrodes are parallelly connected, from positive energy source 21through a common bus 28, transformer winding 23, and plate resistors 29.The screen grids 3| are tied together and positive voltage applied tothem from source 32 through line 33. Cathodes 34 are connected directlyto ground, and the screen grids by-passed to ground through condenser 8.Bias from negative source 2|! is applied to grids 2| through theresistor 9. l

The output of the pulse amplifier I5 is used to drive a switching device36 comprising a plurality of parallelly connected power pulsing tubesAll.

Interposed between the pulse amplifier or line controlled blockingoscillator l5 and the power pulsing tubes 41 is an electronic dischargedevice 35 which acts as a buffer stage. This device, which may be of thedouble tetrode type, is parallell connected and acts as a cathode fol--lower. It receives the output of the blocking oscillator transformer Hfrom the output winding 24 thereof upon its grids 3] through gridresistors 38. Anodes 39 are connected to positive energy source 21through line 28 and plate resistors 40, and the screen grids 4| topositive energy source 32 by line 33. The cathodes 42 are groundedthrough the cathode resistor 43, and the screen grids coupled theretothrough the bypass condenser 44. Negative grid bias for this stage isderived from source 20 through the output winding 24 of transformer H.The input impedance of this stage is relatively fixed and is matchedwith that of the blocking oscillator H: to provide maximum powertransfer.

The pulse developed across the resistor 43 of stage 35 is appliedthrough the grid resistors 46 to the grids 45 of the power pulsing tubes41 which are connected in parallel and which are biased negatively fromsource an through the resistor 50. ground through the capacitor 60 andare supplied with positive energy from source 21 through conductor 28and resistors 49. The plates 5| of these tubes are coupled in parallelto the high potential source 52 through the double throw switch 53 andthe unilateral current-conductin element 54.

One terminal of the secondary winding 55 of transformer 52 is connectedto ground and the other terminal to plate 56 of element 54. The cathode51 of this device, illustrated as a vacuum tube of the diode type, isselectively connected to the plate circuits of tubes 41 through thetwoway switch 53. The blade of this switch is normally closed to contact58, but under certain conditions of circuit operation is closed tocontact 59 to couple the inductance coil 6| into the power pulsingnetwork.

An inductive device 62, which may take the form of an auto transformer,serves as a coupling element and impedance-matching device for the powerpulsing tubes 41 and their load, the ultra high frequency oscillator 53illustrated in the drawing as a split anode magnetron.

Coupled in the primary winding circuit of transformer 62 is a condenser64 which serves the dual purpose of filter and coupling condenser.Common terminal 65 of transformer 52 is connected to ground and itssecondary terminal 65 to the cathode and filaments B1 of oscillator 63.Condenser 64 discharges through the power pulsin tubes 41 into theprimary winding of transformer 52 through ground and terminal 65. Amodulating pulse is therefore induced in the secondary winding oftransformer 62 which is impressed upon the ultra high frequencyoscillator 63, the circuit being completed from terminal 65 throughground to anode 69, thence to cathode El and terminal 66.

In operation, the blocking oscillator network |5 performs the functionof timing the plus modulation of oscillator 63. A trigger pulse ofsuitable characteristics is impressed upon the circuit through inputterminals III for delivery to device it which is normally cut of: by thefixed negative grid potential supplied from source 28. When the triggerpulse is received by grids 2|, they are driven less negative than thecut-oil value, and plate 26 start to draw current. The flow of platecurrent through plate winding 23 of transformer ll induces a voltage ingrid winding IB which in turn drives grids 2| more positive with theresult that the plates draw more current. When this regeneration starts,a steep negative wave front, that is, negative from the grid side ofline to ground, is sent down the blocking lin l2. This wave front hitsthe open Screen grids 48 are by-passed to of Wievmm and =18! b80152:Withhthifli SWMHBSHMVB: phase: to lbw-811G191 ofi time I8; Wi'lem thisnegative woltage appears ow the .grids, the griii voltage becomes lesspositive with: a; rosuitant decrease iniplatewcucrent. platecurrentdecreases,- regeneration isrestabllshed'iinthevoppositerdirectiom and the grids: are: drivennegatiuoly-beynndfiplate current cutwflt: During: tha tinwthat the gridsarm-drawing current, anegative -voliiage ia bufliflupwcross theccndensers: rod lim 121' whloln actsas-adiisd= negative grid: biasiokeepl-th e tubesh'uii oitfduving the: re-- mainder of the: triggerpulseitimaconstant oi th e grid circuit: together-withing add adltime diieto-trigger input impedance is mads--- short compared itathe time betweentrigger signals soz that the grid voltage will have attained itsorigsimi vzalucbetore the next trigger signaliappears.

wmdihg fliis emplbyed in: the transformer-cla cuiir-to -dch'lvem apositive pulse-output: to butter stagesa which OPGIEtiEW-fifi =a=cathbde follower. Since the L cumeniirequirementsl the switchingbranch-38 necessitate the paralrellm oi a pin-- fixedand lsmatthedto-that ofblooltlng oscilla town" Its grids are-biased to cut-om'fromnegative source-2 and} when the'pulsefrom the blocking oscillator isrooeived on'them they aredriven posiiirve anda-high peale current isdrawn through the rmo -inductive resistor-43$ is=-therof0re developed atthe cathodes 4! of" elemerittimed delivercdasatrigger for the tubes 41of switchlhg deviceifitthe function of' which is bestdescribed inconneetion with the power supply-branch.

The circuit is so'synchronized' that the trigger puma Marcitubes fl isreeetvecl aftei the line voltage-Es reaches a positive-peak vaiue; asshownin .Fig. 4. It follows therefore that the tubes 4!: :are. non-cond'llclii've durihg' the positive rise in' linevoltagoin:the-secondary winding 55 of transformer" 52; since: thesetubes arenormallyneg atively. biased: to cutsofi by source as, and accordingl ythey' act'at this moment asan open swituhn.

When the line voltage Er. goes positive; plate 56 of tube 54goes-positive; and the tube becomesconductlng and current is stored inthe filtering condenser ttgithwfiow: being: from ground throughsecondarmwinding '5, the tube, switch'53,'con= denser Bill and theprimary winding of transformerl 62', determined-by the tap -68 and-"tomminainfiibaclczto ground;

Thercaditer, pulse 1 from linezconttolledblockingzoscillator lmisreoelved on the gridsof tubes 41'; driving-them positivebeyond cut-off.As these'tubesbecome conducting, condenser Mdis charges-. throughthemarrd: the primary winding otitransfonmer 62 This develops a-pulse,whose period is determined by and-equai to that of the trigg-ering pulsereceived-by tubes 41," whichv is induced in'the-secondarywindlng oftransformer 62 'andtransmittedtherefrom to the ultra. high frequencyoscillator as a modulating voltage.

Asstat'ed inthe description of the circuit,

A pulse smitchzitlis normally closed to contact 58, andthe operation. ofthe circuit under these conditions is predicated on the fact that thepower supply frequency is substantially equal to the pulse repetition.rate.

the power circuit, since element 54- is;conducting. only during thepositive half cycle of the voltage EL. Since tubes." act as a switch,current flows from power source 52 through them, thence over ground tothe secondary winding 5570f transformer 52. This is objectionable,otcourse, since charging current is diverted from the condenser 64. andsince it also results in an unnecessary dissipation of power. Thecurrentconducting capacities of the elements 41 are limited by theirinherent characteristics, and the additional current drawn from thepower circuit by them: is therefore necessarily dissipated in the'formof heat energy.

With: inductance coillfizi in the power circuit, noappreciablepcurrentis drawn by the tubes 41 from the power source, since itofiers a highimpedance to pulses which are in the order of the triggering pulsedelivered to the power pulsing tubes. Thus, current flow from plate 55to cathode Slrthrough inductance coil 6! to tubes 41 over ground andback through winding 55 is impeded until tubes 41 are non-conducting,and no appreciable amount of current is drawn. by

them; This allows the output of the power circuit to; be stored in thecondenser 64.

Where pulserepetition rates exceed approximately; two and one-half timesthe power supply frequency, it is advisable to resort to an alternatepower-supply method such as a voltage doubling circuit. This arrangementlends itself more readily to proper synchronization for theseconditinns.

Thusfar in: describing the operation of the circult, reference has notbeen made to the fundtinns of;transformer 62. other than that ofstepping; up: the modulating pulse delivered to the ultra highfrequency'oscillator 63. In addition tosthis function, it .also servesas an impedance- 'matching device and; coupling means for the tubes -41.andzrtheir: load 63.

Rreviously;. the: power tubes of vacuum tube modulators: fornultra highfrequency oscillators were connected: directly to'their load in. a.manner similamtolthatssnown in Fig. 2, which fact necessitates theiuseoii large tubes. In actual practice, a-nnmbenzofizthese tubes arenecessary, although only'one; I1, is shown .in the figure. This tube isgreatly enlarged for the purpose of comparing it with tube 41 in Fig. 3to symbolize, though not to: scale, the reduction in size of theseelements made possible by my improved coupling, diagrammecl in Fig. 3.

In the old coupling method illustrated in Fig. 2, attention isdirect'ed'to two elements, coil 13 and unilateral current-conductingdevice 14, whose functions may be described by first considering theoperation of the circuit without them.

As the. line voltage EL starts positive, plate 56 of tube 54 goespositive and so does plate 15 of condenser 64. Since plate It istherefore necessarily negative, anode 69 of element 63 is also negative,and the polarity of this device is reversed. Accordingly, no currentflows and condenser v54 is not charged but is left floating in the line.In order that charging may be effected, it is therefore necessary toprovide a shunt path for the direct current and accordingly an elementsuch as the coil 13 is placed in the circuit. When this is done, theresistance of the shunt path together with the capacitance of element 64form a tuned circuit, and as soon as condenser 64 discharges,oscillations are set up in the circuit which cause an over-shooting inthe pulse. To damp out these oscillations and to prevent over-shooting,the unilateral current-conducting element 14 is placed across the coil13.

In applying my improved coupling means, which is shown in Fig. 3, I amable to simplify the circuit by omitting both of the elements 13 and 74.Here the primary winding of the inductive coupling means 62, defined bythe tap E8 and terminal 65, in addition to other functions provides a'direct current path and no coil, such as 13 (Fig. 2), is necessary.Likewise, element M (Fig. 2) is unnecessary, since the direct currentresistance and the inductance of this primary winding is low, and theobjectionable oscillations found in the prior art circuit are notpresent. Of itself, this is a marked improvement, since element 14 mustbe specially constructed to withstand the high inverse voltage impressedon it and also to meet the high current-conducting requirements of thecircuit.

Further, since the power pulsing elements H are inductively connected totheir load, it is possible to use medium voltages tubes and therebyfurther reduce the size of the apparatus.

To summarize the salient features of the circuit's operation, it may bepointed out that the coupling device employed embodies in one singleelement, illustrated as an auto transformer 62, a, means for directlyperforming the multiple functions of coupling tubes M with their load63, of providing a direct current shunt path for the filtering condenser(i l, of providing an impedance-matching element for tubes 41 andoscillator 63, and that of stepping up the modulating pulse supplied tothis latter element. Collaterally, it permits the use of medium voltagetubes in the place of high voltage tubes heretofore necessary underdirect connected operation.

Likewise, the interpositioning of the buffer stage 35 between the linecontrolled blocking oscillator l and the switching network 35 servesseveral purposes by providing for the accurate pulsing of theoscillator, by acting as an impedance-matching means for the networks I5and 36 and by providing for the delivery of an undistorted trigger pulseto the tubes 41, irrespective of the fact that the highcurrent-conducting requirements of this branch of the circuitnecessitate the paralleling of a plurality of these devices.

Modifications of my invention are, of course, possible and may suggestthemselves from the foregoing disclosure. Accordingly, the embodimentherein described and represented in the accompanying drawing is to beregarded as illustrative. and the spirit and scope of my invention to belimited only by the appendant claims.

What is claimed is:

1. In combination with an ultra high frequency oscillator, a blockingoscillator having connected in the grid circuit thereof a simulatedtransmission line, a butler stage comprising an electronic dischargedevice connected as a cathode follower for receiving the output of saidblocking oscillator, a power pulse switching device comprising aplurality of electronic discharge elements, each with a separate controlgrid driven by the output of said blocking oscillator, an energy storagecondenser, a slnusoidally varying power-supply source, andinterconnections between said switching device, said condenser and saidsource whereby said condenser is alternately charged from said sourceand discharged through said switching device to release energy to saidoscillator. said discharge being synchronized to occur after the peakvalue of said source has been attained.

2. In combination, with an ultra-high-frequency oscillator, a blockingoscillator, a bufler stage having an electronic discharge deviceconnected to receive the output of said blocking oscillator, a powerpulse switching stage having at least one electron discharge devicedriven by the output of said buffer stage, a sinusoidal power-supplysource, a storage condenser connected to receive energy from saidsource, said storage condenser being further connected to release energythereof through said switching device to said oscillator after theattainment of the peak value of said source.

3. In combination, an oscillator to be energized at regular intervals,2. pulse generator, a power pulse switching stage having at least oneelectron discharge device driven by the output of said generator, asinusoidal power-supply source, a storage condenser connected to receiveenergy from said source, an inductive device having primary andsecondary windings, said secondary winding being connected across saidoscillator said storage condenser being further connected to releaseenergy thereof through said switching stage to said primary windingafter the peak value of said source has been attained.

4. In combination, an oscillator to be pulsed, a sinusoidal power-supplysource, a storage condenser connected to receive energy from saidsource, an electron tube switching device having grid and platecircuits, a pulse generator connected to control the grid of saidswitching device and an inductive device having primary and secondarywindings, said oscillator being connected to said secondary winding, theplate circuit of said tube switching device being connected between saidcondenser and said primary winding for periodically releasing the energyof said storage condenser to said oscillator during each positive secondquarter cycle of said source.

5. Apparatus for supplying unidirectional electric pulses to aunidirectional voltage responsive radio-frequency energy generator,comprising first transformer means for receiving alternating currentprimary power and delivering high tension alternating voltage at theterminals of its secondary winding, a rectifier tube and a gridcontrolled tube connected in series between the secondary terminals ofsaid first transformer means, the cathode of one of said tubes beingconnected to the anode of the other and the remaining anode and cathodebeing connected to the secondary terminals, a second transformer havingtwo winding terminals for connection to said radio-frequency energygenerator, a capacitor, said second transformer further having a windingportion connected in series with said capacitor, and means connectingsaid series-connected capacitor and winding portion between 2,4s'aaoathe cathode and the anode of said grid controlled tube.

6. Apparatus as defined in claim 5, further including means forsupplying to the control grid of said tube pulses recurring at thefrequency of the alternating current in said first transformer means,said pulses being timed with the quarter of each cycle during which thevoltage applied to the anode of said rectifier tube is positive butdecreasing in magnitude.

7. Apparatus as defined in claim 5, wherein said second transformer isan auto transformer having a terminal at each extremity of said windingand a connection to an intermediate position of said winding, both endterminals being connected to said radio frequency energy generator, acapacitor, and means connecting said capacitor in series with one ofsaid terminals and said connection, thereby series connecting saidcondenser and a portion of said winding, said means being furtherconnected between the cathode and anode of said grid controlled tube.

8. In combination with a load to be impulsively energized at regularintervals, an inductive device having primary and secondary windings, asinusoidal power supply source, energy storing means connected toreceive energy from said source, and a unidirectional electronicdischarge device having a control grid, said device being connected inseries with said energy storing means and primary winding, said loadbeing connected to said secondary winding, and said control grid of saidelectronic device being synchronized with said sinusoidal source forunidirectionally releasing the energy from said storing means to saidload during each cycle of the sinusoidal variations of said source afterthe peak value thereof has been attained.

pulse generator for periodically releasing energy to said oscillatorafter the attainment of the peak voltage of said source.

DAVID Y. HIM.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,978,461 Hoover Oct. 30, 19342,153,756 Hunt Apr. 11, 1939 2,212,420 Harnett Aug. 20, 1940 2,276,994Milinowski Mar. 17, 1942 2,295,585 Lindquist Sept. 15, 1942 2,351,439Livingston June 13, 1944 2,405,069 Tonks et al July 30, 1946 2,405,070Tonks etal July 30, 1946 FOREIGN PATENTS Number Country Date 460,562Great Britain Jan. 25, 1937

